This invention relates generally to the electrolysis of water, and more specifically, to improved methods and apparatus for the production of oxygen, hydrogen and heat by electrolyzing water.
Hydrogen gas is very important for hydrogenation of chemical compounds, in semiconductor fabrication and in ammonia synthesis, to name but a few uses. It is frequently produced by separating carbon monoxide and hydrogen resulting from high-temperature gasification of coal, or from petroleum products. However, this hydrogen is not sufficiently pure for many applications.
High purity hydrogen is needed in the food industry to produce margarines, for example. Pure oxygen is important in life support systems in hospitals, submarines, space vehicles, and so on. Electrolysis methods are generally recognized for providing high purity products, and water electrolysis methods in particularly are useful in yielding hydrogen and oxygen of sufficient purity for such applications.
Methods for the electrolysis of water are known. One representative electrolytic cell configuration for electrolysis of water would comprise an anode (+) and cathode (xe2x88x92) separated by a physical barrier, e.g., porous diaphragm comprised of asbestos, microporous separator of polytetrafluoroethylene (PTFE), and the like. An aqueous electrolyte containing a small amount of ionically conducting acid or base fills the anode and cathode compartments of the cell. With application of a voltage across the electrodes hydrogen gas is formed at the cathode and oxygen is generated at the anode.
Heretofore, methods of electrolyzing water have had several disadvantages. For example, anodes can form oxides which can passivate with some metals. Cathodes can deposit contaminants like metals, organic residues and particulates, thereby coating, passivating or even changing their electrocatalytic behavior. The bubble size of evolved gases too can be such as to blanket the electrodes with an almost insulating film. These effects lead to higher capital and operating costs due to higher cell voltages as well as losses in current efficiency.
Most processes for electrolyzing water have failed to increase reaction temperatures or generate sufficient heat especially at the electrodes to effectively increase rates of chemical reactions in or at the electrodes, for anode or cathode cleaning, assist in minimizing gas blanketing effects, or enhance the incorporation and storage of hydrogen in cathodes in facilitating the formation of useful metal hydrides, for instance. Because of the above shortcomings, processes for electrolyzing water have not always been conducted under the most economical conditions, for example, at higher current densities.
Accordingly there is a need for improved methods and apparatus for electrolysis of water which are capable of enhancing the generation of oxygen, hydrogen and heat.
In accordance with the invention an improved method is provided for electrolyzing water for enhanced production of oxygen, hydrogen and heat by the steps of:
(i) providing an electrochemical cell comprising an isotopic hydrogen storage cathode, an electrically conductive anode and an ionically conducting electrolyte comprising water, and
(ii) impressing a repeating sequence of voltages across the cathode and anode comprised of at least two cell voltage regimes, a first cell voltage regime consisting of a voltage sufficient to enhance cathodic absorption of hydrogen, and a second cell voltage regime consisting of at least one voltage pulse which is at least 2 times the voltage of the first cell voltage regime for a total duration of no greater than 0.10 seconds.
More particularly, the voltage of the first cell voltage regime will range from about 1 to about 10 volts, and the voltage pulse of the second cell voltage regime will range from 2 times to 1,000 times the voltage of the first cell voltage regime wherein the total duration of the voltage pulse ranges from about 0.5 nanoseconds to 0.10 seconds.
For purposes of this invention xe2x80x9chydrogenxe2x80x9d, which is produced by the cathode and also absorbed by the cathode, is intended to include ordinary hydrogen (H2), and its isotopes, such as D2, T2, HD, HT; Hxe2x88x92, Dxe2x88x92, Txe2x88x92 and their metal hydrides; Hxe2x80xa2, Dxe2x80xa2 and Txe2x80xa2. The term xe2x80x9cwaterxe2x80x9d as appearing in the specification and claims is intended to include ordinary water (H2O), deuterium oxide (D2O), tritium oxide (T2O) and mixtures thereof. Thus, the electrolyte of the foregoing method may comprise in addition to an ionic compound, a solvent selected from water (H2O), deuterium oxide, tritium oxide and mixtures of the same. The ionic compound may include metallic compounds or metal oxy-compounds, such as metal oxydeuterides, metal oxy-triterides, metal hydroxides and mixtures thereof.
The expression xe2x80x9ctotal durationxe2x80x9d for purposes of this invention is intended to include all the time elements of a particular voltage pulse, including rise time, time at or near maximum voltage and fall time.
The term xe2x80x9cenhancedxe2x80x9d or xe2x80x9cenhancingxe2x80x9d as appearing in the specification and claims relative to the production of oxygen, hydrogen and heat is intended to mean optimizing or maximizing their production consistent with achieving the highest economical and practical current efficiency and current density for the generation of oxygen and hydrogen with the simultaneous production of sufficient heat to foster their production.
The methods include steps wherein, for example, the sequences of voltages reciprocate between the first and second voltage regimes, including regimes wherein the second cell voltage regime is dovetailed onto the first cell voltage regime.
It is still a further object of the invention to provide improved methods for the electrolysis of water for enhanced production of oxygen, hydrogen and heat wherein a repeating sequence of voltages includes the step of applying a positive potential sufficient for cleaning the electrodes, which then may be followed, for instance, with the step of applying a negative potential for further cathodic absorption of hydrogen. That is to say, a cathode potential of xe2x88x920.10 to about xe2x88x923 volts and a current density of at least 1.0 mA/cm3 of cathode surface area.
In accordance with the invention it is still a further object to provide for an apparatus for electrolyzing water for the enhanced production of hydrogen, oxygen and heat which comprises:
(i) an electrochemical cell having an isotopic hydrogen storage cathode, an electrically conductive anode and a compartment for holding an ionically conducting electrolyte comprising water, and
(ii) means for applying to the cathode and the anode at least two alternating voltage regimes, a first cell voltage regime consisting of a voltage ranging from about 1 to about 10 volts, and a second cell voltage regime consisting of at least one voltage pulse ranging from 2 times to 1,000 times the voltage of the first cell voltage regime, the total duration of the voltage pulse ranging from about 0.5 nanoseconds to 0.10 seconds.
It is also a further object to provide a pulsed drive system for an electrochemical cell, which comprises means for providing a train of timing pulses, means for counting and decoding the timing pulses, and means for generating alternating pulsed potential sequences across an anode and a cathode of the cell at predetermined times in response to the counted and decoded pulses.